Rotational coupling device with self-contained wet clutch pack

ABSTRACT

A rotational coupling device having a self-contained wet clutch pack and fluid isolated field shell is provided. The device includes a hub disposed about a rotational axis. A rotor is supported on, and configured for rotation about, the hub and defines a radially extending wall and a chamber on one side of the wall surrounding said hub and defining a sump containing a fluid. An armature is supported on the hub for rotation therewith in the chamber and axially spaced from the wall. A field shell is disposed on an opposite side of the rotor wall from the armature and houses a conductor. The field shell is isolated from the fluid in the chamber. Energization of the conductor urges the armature in a first axial direction towards the radially extending wall of said rotor to couple the rotor to the hub for rotation therewith.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/527,474 filed Aug. 25, 2011, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

a. Field of the Invention

This invention relates to a rotational coupling device. In particular,the instant invention relates to a device having a variety ofimprovements intended to permit use of the device in applicationsrequiring either a wet (i.e. including use of a lubricating fluid) ordry coupling device and in applications requiring either vertical orhorizontal mounting arrangements.

b. Background Art

Rotational coupling devices such as clutches and brakes are used tocontrol transfer of torque between rotational bodies. In anelectromagnetic coupling device, an armature coupled to an input oroutput member is brought into engagement with, and/or disengagementfrom, a rotor coupled to the other of the input or output members inorder to rotatably couple or decouple the input and output members.

Conventional electromagnetic coupling devices are often ill-suited touse in certain applications including those where a wet coupling deviceis desired and in applications where the device may need to be orientedvertically. For example, in devices that are oriented vertically,gravitational forces act on the armature and/or clutch plates betweenthe armature and rotor and may cause undesirable movement and frictionalengagement of these components at a time when the torque transfer isundesirable. Further, if the device is oriented vertically and a wetdevice is required, difficulties exist in insuring adequate lubricationof the device components in view of the gravitational forces acting onfluid in the device. It is also difficult to design a wet device inwhich the electromagnetic circuit provides desired operatingcharacteristics. Use of existing devices in someenvironments—particularly those in which water or other liquids may bepresent—can also be problematic because of an inability to adequatelyremove such liquids and maintain the operability of the device.

The inventors herein have recognized a need for a rotational couplingdevice that will minimize and/or eliminate one or more of theabove-identified deficiencies.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a rotational coupling device. Inparticular, the present invention relates to a rotational couplingdevice having a wet clutch pack with a fluid isolated field shell.

A rotational coupling device in accordance with another embodiment ofthe invention includes a hub configured for coupling to a shaft forrotation with the shaft about an axis of rotation. The device furtherincludes a rotor supported on the hub and configured for rotationrelative to the hub about the axis of rotation. The rotor includes afirst member defining a radially extending wall and a chamber on oneside of the radially extending wall surrounding the hub. The chamberdefines a sump containing a fluid. The device further includes anarmature supported on the hub for rotation therewith and disposed withinthe chamber. The armature is disposed on a first side of the radiallyextending wall of the rotor and axially spaced from the radiallyextending wall of the rotor. The device further includes a field shelldisposed about the hub on a second side of the radially extending wallof the rotor opposite the armature. The field shell houses a conductortherein and the field shell and the conductor are isolated from thefluid. Energization of the conductor urges the armature in a first axialdirection towards the radially extending wall of the rotor to couple therotor to the hub for rotation therewith. A rotational coupling device inaccordance with this embodiment of the invention is advantageous ascompared to conventional devices because it provides a more simpledesign for a wet device than conventional devices.

The foregoing and other aspects, features, details, utilities, andadvantages of the invention will be apparent from reading the followingdetailed description and claims, and from reviewing the accompanyingdrawings illustrating features of this invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 are perspective views of a rotational coupling device inaccordance with the present invention.

FIG. 3 is a cross-sectional view of the rotational coupling device inFIGS. 1-2.

FIG. 4 is a plan view of the hub of the device in FIGS. 1-2.

FIG. 5 is a cross-sectional view of the hub of the device in FIGS. 1-2.

FIG. 6 is an enlarged cross-sectional view of a portion of the device inFIGS. 1-2 illustrating the interface between the hub and clutch platesof FIGS. 1-2.

FIG. 7 is a plan view of the rotor of the device in FIGS. 1-2.

FIG. 8 is a perspective view of a portion of the rotor of the device inFIGS. 1-2.

FIG. 9 is an enlarged cross-sectional view of a portion of the device inFIGS. 1-2 illustrating a portion of the rotor of the device in FIGS.1-2.

FIG. 10 is a plan view of the armature of the device in FIGS. 1-2.

FIGS. 11-13 are plan views of various clutch plates of the device inFIGS. 1-2.

FIG. 14 is a plan view of the field shell of the device in FIGS. 1-2.

FIG. 15 is an enlarged cross-sectional view of a portion of the devicein FIGS. 1-2 illustrating the venting of vapor in the device in FIGS.1-2.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein like reference numerals are usedto identify identical components in the various views, FIGS. 1-3illustrate a rotational coupling device 20 in accordance with oneembodiment of the invention. Device 20 functions as a clutch toselectively transfer torque from a rotating shaft (not shown) driven byan engine, electric motor or other conventional power source. Device 20also functions as a brake when torque is not being transferred. Device20 may be provided for use in a lawnmower or similar device. It will beunderstood by those of ordinary skill in the art, however, that device20 may be used in a wide variety of applications requiring a clutchand/or brake. Device 20 may include a hub 22, a spacer 24, a rotor 26, asealing plate 28, an armature 30, a spring 32, clutch plates 34, 36, 38,40, 42, means, such as tubes 44, 46, for transporting fluid from a sumpto clutch plates 34, 36, 38, 40, 42, a field shell 48, a conductor 50,brake plates 52, 54 (see FIG. 14), means, such as magnets 56 for urginga portion of the rotor 26 towards brake plates 52, 54, and a fluidslinger 58.

Hub 22 transfers torque from a rotating shaft (not shown) to armature 30and clutch plates 36, 40. Hub 22 may be made from conventional metalsand metal alloys. Hub 22 is annular and is disposed about the rotatingshaft and an axis 60 of rotation for the shaft. Referring to FIG. 4, aradially inner surface of hub 22 may define a radially inwardlyextending key 62 configured to be received within a corresponding keywayin the rotating shaft to couple hub 22 to the shaft for rotationtherewith. It should be understood that hub 22 may alternatively definea keyway configured to receive a corresponding key in the rotating shaftor may be coupled to the shaft using a variety of other conventionalcoupling methods. The radially outer surface of hub 22 may define aplurality of radially outwardly extending splines 64 configured to bereceived within corresponding notches in armature 30 and clutch plates36, 40. The circumferential spacing between splines 64 may vary as shownin FIG. 4 for a purpose described hereinbelow. Referring now to FIG. 5,a vent bore 66 may extend between the radially inner and outer surfacesof hub 22 for a purpose described hereinbelow. Bore 66 may extend in adirection perpendicular to axis 60. As shown in FIG. 5, the outerdiameter of hub 22 may vary along its axial length. Hub 22 defines anelongate surface 68 at one axial end configured, as illustrated in FIG.3, to receive field shell and rotor bearings 70, 72, and a spacer 74disposed between bearings 70, 72. The same surface 68 is configured toreceive fluid slinger 58. Referring again to FIG. 5, a groove 76 formednear one axial end of surface 68 is configured to receive a retainerring 78 (see FIG. 3) used to facilitate assembly of device 20 andmaintain the position of bearings 70, 72, and other components of device20. The opposite axial end of hub 22 defines a pair of shoulders 80, 82,configured, as illustrated in FIG. 3, to receive another rotor bearing84 and a fluid seal 86. Referring again to FIG. 5, hub 22 furtherdefines a groove 88 configured to receive a retainer ring which anchorsthe end of spring 32.

In accordance with one embodiment of the invention, hub 22 furtherincludes means, such as shoulders 90, 92, 94, for limiting movement ofclutch plates 36, 40 and armature 30 in one axial direction. The outerdiameter of hub 22 varies to define steps and shoulders 90, 92, 94, withthe diameter increasing moving axially from clutch plate 36 to armature30 such that the radial distances from axis 60 to shoulder 90, 92, 94are different. When device 20 is oriented vertically, gravitationalforce urges armature 30 and clutch plates 36, 40, in one axial direction(to the right in FIG. 3). When the clutch of device 20 is disengaged,therefore, gravitational force may result in undesirable contact amongarmature 30 and clutch plates 34, 36, 38, 40, 42. Referring to FIG. 6,shoulders 90, 92, 94 limit movement of plates 36, 40 and armature 30 toprevent such contact.

Referring again to FIG. 3, spacer 24 is provided to retain bearing 84 inassembled relation to the other components of device 10. Spacer 24 maybe made from conventional metals and metal alloys. Spacer 24 is disposedabout axis 60 and is generally cylindrical in shape. Spacer 24 isconfigured to receive a fastener (not shown) that extends through spacer24 and into the rotating shaft. Spacer 24 may define a head 96 at oneaxial end. Referring to FIG. 1, head 96 may have a plurality of flats 98that allow the rotating shaft to be secured while applying torque to thefastener. Head 96 also opposes shoulder 80 in hub 22 to prevent axialmovement of bearing 84. Spacer 24 may further define a keyway in aradially outer surface configured to receive key 62 of hub 22.

Rotor 26 provides a means for transferring torque to an output member.Rotor 26 provides a reaction surface against which armature 30compresses clutch plates 34, 36, 38, 40, 42 to couple rotor 26 to hub 22for rotation with hub 22. In accordance with another aspect of theinvention as discussed below, rotor 26 may also function as a part of abrake for the output member when the clutch is disengaged. Rotor 26 isdisposed about hub 22 and axis 60 and may include several members 100,102, 104 which may be made from conventional metals and metal alloys.

Member 100 is annular in shape and disposed about axis 60. Member 100defines a radially extending wall 106. Wall 106 defines radially outerand inner circular recesses 108, 110 in one axial side of wall 106.Outer recess 110 is configured to receive a portion of member 102 ofrotor 26. Inner recess 108 is configured to receive sealing plate 28.Wall 106 further defines a plurality of apertures 112 extending axiallytherethrough and in communication with outer recess 110. Apertures 112are configured to receive fasteners 114, 116 used to couple member 100to member 102 of rotor 26. In the illustrated embodiment, fasteners 114,116, comprise screws secured in place by nuts 118, 120, respectively. Itshould be understood, however, that other types of fasteners such asbolts, pins, welds or adhesives could alternatively be used. Fasteners114, 116 extend through a gasket 122 that functions as a seal betweenmembers 100, 102. Fasteners 116 are longer than fasteners 114 and extendthrough spacers 124 used to support leaf springs 126. Each of fasteners116 is used to secure one end of a corresponding leaf spring 126extending between members 100, 104 of rotor 26 for a purposed describedhereinbelow. Referring to FIG. 7, wall 106 may further include one ormore radially spaced rows of circumferentially spaced, banana shapedslots 128. Upon energization of conductor 50, slots 128 help to directthe flow of magnetic flux between wall 106 of member 100 of rotor 26 andarmature 30. In the illustrated embodiment, wall 106 includes a singlerow of three slots 128. It should be understood, however, that thenumber of rows of slots 128 the number of slots 128 in any one row, andthe size and shape of slots 128 may vary. Referring again to FIG. 3,slots 128 are in communication with inner recess 108. Member 100 furtherdefines an axially extending radially inner rotor pole 130 extendingfrom a radially inward end of wall 106. Pole 130 is supported on rotorbearing 72 and includes a radially inwardly extending flange 132 at oneaxial end opposite wall 106 to limit movement relative to bearing 72.

In accordance with another aspect of the invention, member 100, togetherwith member 102, forms a substantially enclosed chamber 134 housingarmature 30, clutch plates 34, 36, 38, 40, 42 and a lubricating fluidsuch as oil. Accordingly, device 20 is not dependent upon fluidintegration with other devices to provide lubricating fluid and does notrequire the design of custom housings for different applications. Member102 is annular in construction and has a diameter that generallyincreases from one axial end 136 of member 102 farthest from member 100to an opposite axial end 138 adjacent member 100. Member 102 defines anaxially ending wall 140 proximate end 136 sized to receive bearing 84and seal 86. Wall 140 defines a radially inwardly extending flange atone end configured to retain bearing 84. A wall 142 extends radiallyfrom the opposite end of axially extending wall 140. Wall 142 forms thebottom of a fluid sump when device 20 is oriented vertically. Fluid maybe inserted or removed through a fill port 144 in which a plug 146 isdisposed. Another axially extending wall 148 extends from the oppositeend of radially extending wall 142. Wall 148 may be configured tosupport an output member 150. In the illustrated embodiment member 150comprises a pulley. It should be understood, however, that member 150could take on a variety of forms including gears. Another wall 152extends from axially extending wall 148 in a generally radial direction,but at an angle to axis 60. Wall 152 terminates in another axiallyextending wall 154. Referring now to FIG. 8, in accordance with oneembodiment of the invention, wall 154 may include means, such asshoulders 156, 158, 160 for limiting movement of clutch plates 34, 38,42 in one axial direction. Wall 154 may define a plurality of axiallyextending grooves 161 in a radially inner surface configured to receivecorresponding teeth 181 on clutch plates 34, 38, 42 (see FIG. 11). Atone or more circumferentially spaced sections, however, a set (equal innumber to the number of clutch plates 34, 38, 42) of adjacent groovesare axially shortened to define shoulders 156, 158, 160. In theillustrated embodiment, grooves 161 are axially shortened in threeequally circumferentially spaced sections on wall 154. It should beunderstood, however, that the number of sections may vary. The axiallength of the grooves 161 in which shoulders 156, 158, 160 are formedvaries to maintain a predetermined spacing between clutch plates 34, 38,42 when the clutch is disengaged. When device 20 is oriented vertically,gravitational force urges clutch plates 34, 38, 42 in one axialdirection (to the right in FIG. 3). When the clutch of device 20 isdisengaged, therefore, gravitational force may result in undesirablecontact among clutch plates 34, 36, 38, 40, 42 and armature 30. Theshoulders 156, 158, 160 on wall 154 limit movement of plates 34, 38, 42to prevent such contact. Referring again to FIG. 3, a radially outwardlyextending flange 162 extends from wall 154 and is configured to bereceived within recess 110 of member 100. Flange 162 defines a pluralityof apertures configured to received fasteners 114, 116.

Member 104 defines an axially extending, radially outer rotor pole 164.Member 104 may comprise a unitary body (i.e. a single piece structurewithout any type of fasteners such as screws, adhesives or welds tocouple multiple pieces together). Referring to FIG. 9, pole 164 definesa coupling surface 166 at one axial end configured to engage acorresponding coupling surface 168 formed in wall 106 of member 100.Member 104 further defines a radially extending flange 170 extendingfrom pole 164. In accordance with one aspect of the invention, flange170 defines a braking surface 172 configured to engage a correspondingbraking surfaces on brake plates 52, 54. Referring to FIG. 2, flange 170further defines a plurality of apertures 174 through which fasteners 176such as rivets may extend with each fastener 176 coupled to one end of acorresponding leaf spring 126. When the clutch is disengaged, member 104is urged in one axial direction towards brake plates 52, 54 (to the leftin FIGS. 3 and 9) as discussed hereinbelow such that coupling surface166 disengages from coupling surface 168 and braking surface 172 engagesthe braking surfaces on brake plates 52, 54. As a result, a fluid flowopening is created between the coupling surfaces 166, 168 on members104, 100, which permits drainage of any fluid (e.g. water) fromoperating in wet environments. When the clutch is engaged, member 104 isdrawn in an opposite axial direction towards member 100 (to the right inFIGS. 3 and 9) by electromagnetic attraction such that braking surface172 disengages from the braking surfaces on brake plates 52, 54, andcoupling surface 166 engages coupling surface 168 on member 100. Theintegration of the rotor outer pole 164 and braking surface 172 providesa simpler design than conventional devices and also provides anefficient way for removing liquids from device 20 when device 20 is usedin a wet environment. Further, the design minimizes the time that boththe brake is applied and the clutch is engaged during transitionsbetween engagement and disengagement of the clutch thereby avoidingundesirable wear and heat. The design also increases the speed ofdisengagement of the brake and engagement of the clutch relative toconventional designs thereby providing an improved feel to the user.

Referring again to FIG. 3, in accordance with another aspect of theinvention, means, such as sealing plate 28, are provided to preventfluid from exiting chamber through slots 128 in member 100 of rotor 26.Plate 28 is ring shaped and configured to be received within recess 108in member 100 of rotor 26. Plate 28 is made from a non-magnetic materialor a material having a greater magnetic reluctance than member 100 ofrotor 26. The construction of member 100 of rotor 26 and plate 28 allowsthe use of slots 128 in member 100, and the increased strength in theelectromagnetic circuit resulting from their use, in applicationsrequiring a wet device. To prevent fluids from gathering in slots 128 onthe opposite side of plate 28 from chamber 134 when device 20 is used ina wet environment, an epoxy may be used to fill slots 128.

Armature 30 is provided to engage the clutch by urging plates 34, 36,38, 40, 42 into frictional engagement. Armature 30 may be made frommetals or metal alloys or other materials having relatively low magneticreluctance. In one accordance with one aspect of the invention, however,the radially innermost portion of armature 30 may be made from amaterial having a higher magnetic reluctance than the rest of armature30 to limit or prevent flux transfer to hub 22 and undesirableelectromagnetic attraction between armature 30 and hub 22. Armature 30is disposed about hub 22 and axis 60 on one axial side of wall 106 ofrotor 26. Referring to FIG. 10, armature 30 is annular in shape anddefines a plurality of notches 178 in a radially inner surfaceconfigured to engage splines 64 on hub 22. Armature 30 further defines aplurality of circumferentially spaced fluid apertures 180 between theradially inner and outer surfaces of armature 30. Apertures 180 may besized to receive tubes 44, 46 as discussed in greater detailhereinbelow. Apertures 180 may be nearer a radially inner diameter orsurface of armature 30 than a radially outer diameter or surface ofarmature 30.

Referring again to FIG. 3, in accordance with another aspect of theinvention, spring 32 may be used to bias armature 30 in one axialdirection (to the left in FIG. 3) to counteract an opposinggravitational force biasing armature 30 in the opposite axial direction(to the right in FIG. 3) when device 20 is oriented vertically. Spring32 may be made from conventional metals and metal alloys. One end ofspring 32 may be positioned against a retaining ring disposed withingroove 88 in hub 22 while the opposite end of spring 32 engages armature30. The use of spring 32 permits faster engagement of the clutch becausearmature 30 does not have to overcome the gravitational force biasingarmature 30 away from clutch plates 34, 36, 38, 40, 42.

Clutch plates 34, 36, 38, 40, 42 are provided to transfer torque fromhub 22 to output member 150 by coupling rotor 26 to hub 22 for rotation.Clutch plates 34, 36, 38, 40, 42 may be made from conventional metalsand metal alloys and be treated for wear and corrosion resistance usingthe process offered under the registered trademark “NITROTEC” by TTIGroup Ltd. of the United Kingdom or equivalents. Clutch plates 34, 36,38, 40, 42 are disposed between armature 30 and radially extending wall106 of member 100 of rotor 26. In the illustrated embodiment, threeclutch plates 34, 38, 42 are coupled to member 102 of rotor 26 forrotation therewith, but are axially movable relative to member 102 ofrotor 26 while two clutch plates 36, 40 are coupled to hub 22 forrotation therewith, but are axially movable relative to hub 22. Each ofplates 36, 40, is disposed between a corresponding pair 34, 38, and 38,42, respectively of plates 34, 38, 42. It should be understood that thenumber and ordering of clutch plates may vary. Springs (not shown) maybe disposed between plates 34, 36, 38, 40, 42 to prevent rattle.

Referring to FIG. 11, clutch plates 34, 38, 42 are annular in shape anddefines a plurality of teeth 181 in a radially outer surface configuredto engage corresponding teeth on a radially inner surface of wall 154 ofmember 102 of rotor 26. Plates 34, 38, 42 further define a pair ofradially spaced rows of circumferentially spaced, banana shaped slots182. Upon energization of conductor 50, slots 182 serve to directmagnetic flux to travel between wall 106 of rotor 26 and armature 30along the radially inner and outer peripheries of plates 34, 38, 42. Itshould be understood that the number of slots 182 in any one row, andthe size and shape of slots 182 may vary.

Referring now to FIGS. 12-13, clutch plates 36, 40 are annular in shapeand define a plurality of circumferentially spaced notches 184, 186,respectively, in a radially inner surface configured to receive splines64 on hub 22. Plates 36, 40 further define a pair of radially spacedrows of circumferentially spaced, banana shaped slots 188, 190,respectively. As with slots 182 in plates 34, 38, 42, upon energizationof conductor 50, slots 188, 190 serve to direct magnetic flux to travelbetween rotor 26 and armature 30 along the radially inner and outerperipheries of plates 36, 40. It should be understood that the number ofslots 188, 190 in any one row, and the size and shape of slots 188, 190may vary. Plates 36, 40 further define a plurality of circumferentiallyspaced fluid apertures 192, 194 respectively, disposed radially betweenthe radially inner surface of plates 36, 40 and the radially inner rowof slots 188, 190, respectively. Apertures 192, 194 permit passage offluid for lubrication of plates 34, 36, 38, 40, 42.

In accordance with another aspect of the invention, the circumferentialspacing between notches 184, 186 on clutch plates 36, 40 varies suchthat a circumferential gap d_(1a), d_(1b) between a pair of adjacentnotches 184, 186 on each plate 36, 40 is greater than a circumferentialgap d_(2a), d_(2b) between other pairs of notches 184, 186 on each plate36, 40. Similarly, the circumferential spacing between adjacent fluidapertures 192, 194 on each of clutch plates 36, 40, varies such that acircumferential gap d_(3a), d_(3b) between a pair of apertures 192, 194,on each plate 36, 40 is greater than a circumferential gap d_(4a),d_(4b) between other pairs of apertures 192, 194, on each plate 36, 40.Further, the center of the circumferential gap d_(3a) between apertures192 in plate 36 is located at a point radially outwardly of a center ofthe circumferential gap d_(1a) between notches 184 in plate 36 while thecircumferential gap d_(3b) between apertures 194 in plate 40 is locateddiametrically opposite a point that is radially outwardly of a center ofthe circumferential gap d_(1b) between notches 186 in plate 40. Thedifferent arrangement of the fluid apertures 192, 194 relative tonotches 184, 186 in plates 36, 40 facilitates proper assembly of device20 by providing a visual cue to the proper ordering of plates 36, 40.

In accordance with another aspect of the invention, means, such as fluidtransport tubes 44, 46, for transporting fluid from the sump to clutchplates 34, 36, 38, 40, 42 are provided. Referring to FIGS. 3 and 10,tubes 44, 46 extend through apertures 180 in armature 30. In theillustrated embodiment two tubes are used that extend throughdiametrically opposite apertures 180 and are therefore diametricallyopposite one another. It should be understood, however, that the numberof tubes and their orientation may vary. Referring to FIG. 3, each tube44, 46 has one end 196 defining a fluid inlet and submerged in the fluidin the sump. Each tube 44, 46 further extends through a correspondingaperture 180 in armature 30 and has an opposite end 198 defining a fluidoutlet disposed within apertures 180 in armature 30 or on an oppositeside of armature 30 from the fluid inlet. The fluid inlet and outlet maybe oriented such that a direction of fluid flow through the inlet isdifferent than a direction of fluid flow through the outlet. Inparticular, the direction of fluid flow through the inlet may beperpendicular to the direction of fluid flow through the outlet. Asshown in FIG. 3, fluid may exit the outlet in a direction parallel tothe rotational axis 60. Referring to FIG. 10, fluid may enter the inletin a circumferential direction relative to the axis of rotation.Alternatively, tubes 44, 46 may be oriented such that fluid enters theinlet in a radial direction relative to the axis of rotation,particularly in applications where device 20 has a horizontalorientation. Rotation of armature 30 enables ends 196 of tubes 44, 46 toscoop fluid from the sump and draws fluid through tubes 44, 46, where itmay be deposited onto clutch plates 34, 36, 38, 40, 42.

Referring again to FIG. 3, field shell 48 is provided to house conductor50. Shell 48 also forms part of an electromagnetic circuit that causesthe selective engagement of wall 106 of member 100 of rotor 26, armature30, and clutch plates 34, 36, 38, 40, 42 to rotatably couple hub 22 androtor 26. Field shell 48 may be made from conventional metals and metalalloys, including steel. Shell 48 is cylindrical and is disposed abouthub 22 and axis 60 and is supported on an outer race of field shellbearing 70. Referring to FIGS. 2 and 3, shell 48 is fixed againstrotation and includes members 200, 202, 204, 206. In accordance with oneaspect of the invention, shell 48 is disposed on an opposite side ofwall 106 of rotor 26 relative to armature 30 and clutch plates 34, 36,38, 40, 42 and is isolated from the fluid in chamber 134. As a result,the design of device 20 is less complex than conventional designsbecause no fluid seals or other methods to prevent exposure to fluidsare required around the conductor 50 or any electrical connections.

Member 200 is generally U-shaped in cross-section and defines axiallyextending, radially inner and outer poles 208, 210 with a radiallyextending end wall 212 extending therebetween. Member 200 is sized toreceive member 202 and conductor 50 between poles 208, 210. Inner pole208 is axially aligned with inner pole 130 of rotor 26 while outer pole210 is disposed radially inwardly of outer pole 164 of rotor 26. Inaccordance with another aspect of the invention, the stampings formember 200 of field shell 48 and member 100 of rotor 26 share a commonpocket design for field shell bearing 70 and rotor bearing 72,respectively, and may be made from the same blank size with a commontool and then press and formed to the desired shape and form.

Member 202 is annular in construction and is disposed within member 200radially between inner and outer filed shell poles 208, 210. Member 202is configured to receive conductor 50. Member 202 is supported on innerfield shell pole 208. Member 202 forms a part of the electromagneticcircuit referred to hereinabove and, like inner pole 208 of member 200,directs magnetic flux from inner rotor pole 130 to end wall 212 ofmember 200 as well as to the outer diameter of inner field shell pole208. The inner diameter of member 202 may vary to define a shoulder 214intermediate the axial ends of member 202. In accordance with one aspectof the invention, a portion 216 of the inner pole 208 of member 200 maybe deformed (e.g. by staking) to limit axial movement of member 202 inone axial direction (to the right in FIG. 3). The outer diameter ofmember 202 may also vary such that member 202 defines a radiallyoutwardly extending flange 218 at one axial end configured to engageconductor 50 and prevent movement of conductor 50 in one axial direction(to the right in FIG. 3).

In accordance with another aspect of the invention, members 200, 202define a fluid passage 220 configured to remove moisture from one axialside of bearing 70. When device 20 is used in wet environments andmounted vertically, the possibility exists for fluid to accumulate onone side of bearing 70 between hub 22 and field shell 48. A fluidpassage 220 is therefore formed including a bore extending from aradially inner surface of inner pole 208 to a radially outer surface ofpole 208 and a space between members 200, 202 to divert fluid frombearing 70 and, ultimately, expel such fluid through the fluid flowopening between coupling surfaces 166, 168, on members 104, 100 of rotor26.

Referring to FIG. 14, members 204, 206 provide a means for mountingbrake plates 52, 54 and provide a means for fixing field shell 48against rotation. Members 204, 206 extend radially outwardly from member200 and are affixed to member 200 by welds or other fasteners. Members204, 206, may be identical in construction. Each of members 204 206defines a slot 222 proximate one circumferential end configured toreceive a bolt or other fastener to counteract field shell rotation.Each member 204, 206 further defines a pair of circumferentially spacedapertures configured to receive fasteners 224 extending axiallytherethrough and into brake plates 52, 54.

Referring again to FIG. 3, conductor 50 is provided to create anelectromagnetic circuit among rotor 26, armature 30 and field shell 48in order to cause armature 30 to move in one axial direction (to theleft in FIG. 3) and press clutch plates 34, 36, 38, 40, 42 intofrictional engagement in order to couple wall 106 of member 100 of rotor26 to hub 22 for rotation therewith. Conductor 50 may comprise aconventional aluminum coil although other conventional conductors mayalternatively be used. Conductor 50 is disposed within a housing 226that may be used to mount conductor 50 within field shell 48. Housing226 may be molded from conventional plastics and, referring to FIG. 14,includes anti-rotation pins 228 extending through apertures in end wall212 of member 200 of field shell 48. Housing 226 may further include anintegral terminal connector 230 through which conductor 50 may beelectrically connected to a power source. Referring again to FIG. 3, inaccordance with one aspect of the invention, the terminal connector 230may be configured such that it slopes away from axis 60 in order toallow gravity to direct any moisture radially outward when device 20 isoperated in wet environments. Conductor 50 and housing 226 are generallyannular and are disposed about hub 22 and axis 60 within field shell 48.In particular, conductor 50 and housing 226 are disposed between theinner and outer poles 208, 210 of shell 48 and end wall 212 and aresupported on member 202 of shell 48. Upon energization of conductor 50,an electromagnetic circuit is formed between wall 106 of member 100 ofrotor 26, armature 30 and field shell 48. Magnetic flux flows from outerpole 210 of shell 48 across an air gap to outer pole 164 of rotor 26.Flux then travels from outer rotor pole 164 to wall 106 of member 100 ofrotor 26 across another air gap. Flux then travels across a radiallyouter portion of clutch plates 34, 36, 38, 40, 42 to armature 30 andback to wall 106 and inner rotor pole 130 across a radially innerportion of clutch plates 34, 36, 38, 40, 42. A portion of this flux alsotravels into member 202 of field shell 48 across air gaps between wall106 and member 202 and between pole 130 and member 202. Flux thentravels from inner rotor pole 130 and member 202 of field shell 48across air gaps to inner field shell pole 208 and end wall 212 andreturns through end wall 212 of field shell 48. Although the illustratedembodiment employs an electromagnetic circuit having two poles, itshould be understood that the circuit could alternatively employ morepoles (e.g. four or six poles).

Brake plates 52, 54 provide a means for applying a braking torque torotor 26 when conductor 50 is deenergized. Brake plates 52, 54 may bemade from conventional materials having a relatively low magneticreluctance including conventional metals and metal alloys such as steel.Referring to FIG. 14, brake plates 52, 54 extends about at least aportion of the circumference of device 20, and preferably only a portionof the circumference of device 20, and are coupled to members 204, 206,of field shell 48. In particular, brake plates 52, 54 are coupled tomembers 204, 206 and suspended therefrom using fasteners 224. Referringto FIG. 9, brake plates 52, 54 define a braking surface 232 configuredto engage braking surface 172 of member 104 of rotor 26 upondeenergization of conductor 50. Brake plates 52, 54, also define aplurality of bores 234 configured to receive magnets 56. Bores 234extend through an axial portion of brake plates 52, 54 and compriseclosed bores as shown in the illustrated embodiment. Referring to FIG.14, brake plates 52, 54 may further define a plurality of slots 236between tabs 238 in which the magnets 56 are disposed in order tomagnetically isolate each magnet from other magnets.

Magnets 56 are provided to create a magnetic circuit between brakeplates 52, 54 and member 104 of rotor 26 to draw member 104 intoengagement with brake plates 52, 54 and provide a braking torque torotor 26 and output member 150. Magnets 56 may comprise neodymium ironboron (Nd—Fe—B) magnets or other known permanent magnets. Magnets 56 maybe embedded within bores 234 of brake plates 52, 54 and may be securedtherein using an adhesive. Magnets 56 may be arranged such that one faceof the magnet 56 is flush with one side (and the braking surface 232) ofbrake plates 52, 54. By placing the magnets 56 such that one face isflush with the engagement surface of brake plates 52, 54 magnets 56 addto the wear surface of brake plates 52, 54 increasing their wearresistance and the braking surface. Magnets 56 may be circumferentiallyspaced from one another about the circumferential extent of brake plates52, 54 and each magnet 56 may be disposed in a tab 238 of brake plates52, 54, separated by slots 236 in brake plates 52, 54. Alternatively,more than one magnet 56 may be disposed in a single tab 238 (and/orslots 236 eliminated) provided that the magnets 56 are appropriatelyspaced from one another. Magnets 56 may also be disposed in every othertab 236 to increase wear surface. It will further be appreciated thatthe number and location of magnets 56 within brake plates 52, 54 mayvary depending upon the characteristics of device 20 and related designrequirements. Magnets 56 may be arranged such that the facing poles ofadjacent magnets 56 are of like polarity thereby forming parallelmagnetic circuits. Alternatively, magnets 56 may be arranged such thatthe facing poles of adjacent magnets 56 are of opposite polarity therebyforming a less efficient series magnetic circuit. Magnets 56 are axiallyaligned with flange 170 of member 104 of rotor 26 such that magneticflux travels axially through magnets 56. In particular, magnetic fluxtravels through one pole of each magnet 56 (located at the radial centerof magnet 56) across an air gap into member 104 of rotor 26. Fluxcontinues to travel radially inwardly and outwardly along member 104 andthen axially across an air gap and radially through brake plates 52, 54to return to an opposite pole of each magnet 56 located on the oppositeaxial end of magnet 56).

In accordance with another aspect of the invention, brake plates 52, 54,and their associated magnets 56 are asymmetrically arranged. Inparticular, brake plates 52, 54 are not diametrically opposed from oneanother, and the circumferential center of brake plate 52 is less thanone hundred and eighty degrees from the circumferential center of brakeplate 54. Upon energization of conductor 50, a portion of member 104 ofrotor 26 circumferentially opposite brake plates 52, 54, is able toquickly engage wall 106 of member 100 of rotor 26, tipping member 104relative to axis 60 thereby increasing the air gap between the brakingsurfaces 172, 232 of member 104 and brake plates 52, 54 and weakeningthe magnetic circuit between magnets 56 and member 104 and reducingclutch engagement time.

Referring to FIG. 15, fluid slinger 58 is provided to direct the returnof fluid to the sump. Slinger 58 may be made from conventional metal andmetal alloys having a relatively high magnetic reluctance includingstainless steel or aluminum. Slinger 58 is disposed about hub 22 on anopposite side of clutch plates 34 36 38, 40, 42 from armature 30.Slinger 58 is disposed radially between hub 22 and wall 106 of member100 of rotor 26. In accordance with one aspect of the invention, ventbore 66 is disposed on an opposite side of slinger 58 from clutch plates34, 36, 38, 40, 42 to permit venting of vapor to equalize systempressure. Vent bore 66 is disposed axially between fluid slinger 58 androtor bearing 72. Vapor from chamber 134 travels through a small opening240 between the radially outer periphery of slinger 58 and member 100 ofrotor 26, through a passage 242 formed between slinger 58 and bearing 72and through vent bore 66. In applications where device 20 is orientedhorizontally, slinger 58 may be replaced by a conventional seal andfluid is distributed by the slinger action of clutch plates 34, 36, 38,40, 42.

While the invention has been shown and described with reference to oneor more particular embodiments thereof, it will be understood by thoseof skill in the art that various changes and modifications can be madewithout departing from the spirit and scope of the invention.

1. A rotational coupling device, comprising: a hub configured forcoupling to a shaft for rotation with said shaft about an axis ofrotation; a rotor supported on said hub and configured for rotationrelative to said hub about said axis of rotation, said rotor including afirst member defining a radially extending wall and a chamber on oneside of said radially extending wall surrounding said hub, said chamberdefining a sump containing a fluid; an armature supported on said hubfor rotation therewith and disposed within said chamber, said armaturedisposed on a first side of said radially extending wall of said rotorand axially spaced from said radially extending wall of said rotor; and,a field shell disposed about said hub on a second side of said radiallyextending wall of said rotor opposite said armature, said field shellhousing a conductor therein and said field shell and said conductorisolated from said fluid wherein energization of said conductor urgessaid armature in a first axial direction towards said radially extendingwall of said rotor to couple said rotor to said hub for rotationtherewith.
 2. The rotational coupling device of claim 1, wherein saidradially extending wall of said rotor includes a slot extending axiallytherethrough between a radially innermost surface of said rotor and aradially outermost surface of said rotor and further comprising asealing plate configured to prevent fluid from flowing through saidslot, said sealing plate having a higher magnetic reluctance than saidradially extending wall of said rotor.
 3. The rotational coupling deviceof claim 1, wherein said radially extending wall of said rotor includesa slot extending axially therethrough between a radially innermostsurface of said rotor and a radially outermost surface of said rotor andfurther comprising means for preventing fluid from flowing through saidslot, said preventing means having a higher magnetic reluctance thansaid radially extending wall of said rotor.
 4. The rotational couplingdevice of claim 1, wherein said rotor includes a second member coupledto said first member and configured for rotation with said first member,said first and second members defining said chamber.
 5. The rotationalcoupling device of claim 4, wherein said second member defines a pulley.6. The rotational coupling device of claim 1, further comprising: afirst clutch plate disposed axially between said radially extending wallof said rotor and said armature, said first clutch plate coupled to saidhub for rotation therewith, but axially movable relative to said hub;and, a second clutch plate disposed axially between said radiallyextending wall of said rotor and said armature, said second clutch platecoupled to said rotor for rotation therewith, but axially movablerelative to said rotor.
 7. The rotational coupling device of claim 6,wherein said armature and said first and second clutch plates areconfigured for movement in a first axial direction towards said radiallyextending wall of said rotor upon energization of said conductor tothereby cause frictional engagement of said first and second clutchplates and coupling of said rotor to said hub for rotation therewith andare configured for movement in a second axial direction opposite saidfirst axial direction upon subsequent deenergization of said conductor,at least one of said hub and said rotor defining a first shoulderconfigured to limit movement of a corresponding one of said first andsecond clutch plates in said second axial direction.
 8. The rotationalcoupling device of claim 6, wherein said armature and said first andsecond clutch plates are configured for movement in a first axialdirection towards said radially extending wall of said rotor uponenergization of said conductor to thereby cause frictional engagement ofsaid first and second clutch plates and coupling of said rotor to saidhub for rotation therewith and are configured for movement in a secondaxial direction opposite said first axial direction upon subsequentdeenergization of said conductor, at least one of said hub and saidrotor including means for limiting movement of a corresponding one ofsaid first and second clutch plates in said second axial direction. 9.The rotational coupling device of claim 6, further comprising a firsttube having a first end submerged in said fluid and extending through afirst aperture in said armature wherein rotation of said armature drawsfluid through said first tube and onto said first and second clutchplates.
 10. The rotational coupling device of claim 6, furthercomprising means for transporting said fluid from said sump to saidfirst and second clutch plates.
 11. The rotational coupling device ofclaim 6, further comprising a fluid slinger disposed about said hub onan opposite side of said first and second clutch plates from saidarmature wherein said hub includes a vent bore extending from a radiallyouter surface of said hub to a radially inner surface of said hub, saidvent bore disposed on an opposite side of said fluid slinger from saidfirst and second clutch plates.
 12. The rotational coupling device ofclaim 6, wherein said first clutch plate includes: a plurality ofcircumferentially spaced notches in a radially inner surface configuredto receive a corresponding plurality of radially outwardly extendingsplines on said hub, a circumferential gap between a first notch of saidplurality of notches and a second notch of said plurality of notchesadjacent to said first notch greater than a circumferential gap betweensaid second notch and a third notch of said plurality of notchesadjacent to said second notch; and, a plurality of circumferentiallyspaced fluid apertures disposed radially outwardly of said plurality ofnotches, a circumferential gap between a first fluid aperture of saidplurality of fluid apertures and a second fluid aperture of saidplurality of fluid apertures adjacent to said first fluid aperturegreater than a circumferential gap between said second fluid apertureand a third fluid aperture of said plurality of fluid apertures adjacentto said second fluid aperture wherein a center of said circumferentialgap between said first and second fluid apertures is located at either apoint radially outward of a center of said circumferential gap betweensaid first and second notches or diametrically opposite said point. 13.The rotational coupling device of claim 1, further comprising a firstbrake plate and wherein said rotor includes a first member defining saidradially extending wall and an axially extending, radially inner rotorpole, said radially extending wall defining a first rotor couplingsurface; and, a second member coupled to said first member for rotationtherewith, but axially movable relative to said first member, saidsecond member defining an axially extending, radially outer rotor pole,a second rotor coupling surface and a first braking surface; said fieldshell defines radially spaced inner and outer field shell poles alignedwith said inner and outer rotor poles, respectively, energization ofsaid conductor establishing an electromagnetic circuit among said fieldshell, said rotor and said armature to urge said armature in said firstaxial direction; said first brake plate defines a second braking surfacealigned with said first braking surface of said second member of saidrotor; and said second member of said rotor is configured such that,upon energization of said conductor, said second member of said rotor isurged towards said first member of said rotor and said second rotorcoupling surface is urged into engagement with said first rotor couplingsurface and, upon deenergization of said conductor, said second memberof said rotor is urged towards said first brake plate, said firstbraking surface is urged into engagement with said second brakingsurface and said second rotor coupling surface is urged to disengagefrom said first rotor coupling surface to create a fluid flow openingbetween said first and second members of said rotor.
 14. The rotationalcoupling device of claim 13, further comprising a permanent magnetcoupled to said first brake plate, said permanent magnet establishing amagnetic circuit including said first brake plate and said second memberof said rotor.
 15. The rotational coupling device of claim 13, furthercomprising a second brake plate defining a third braking surface alignedwith said first braking surface of said second member of said rotor. 16.The rotational coupling device of claim 15, wherein a circumferentialcenter of said first brake plate and a circumferential center of saidsecond brake plate are circumferentially spaced less than one hundredand eighty degrees apart.
 17. The rotational coupling device of claim 1,further comprising a spring biasing said armature in said first axialdirection, said spring configured to counteract an opposing forcebiasing said armature in a second axial direction opposite said firstaxial direction.
 18. The rotational coupling device of claim 1, whereinsaid field shell includes: a first member defining axially extending,radially inner and outer field shell poles; and, a second memberdisposed within said first member radially between said radially innerand outer field shell poles and configured to receive said conductorwherein said inner field shell pole of said first member is configuredto prevent movement of said second member of said field shell in asecond axial direction opposite said first axial direction.